BUENOS AIRES (Reuters) - Cash-strapped Argentina posted a fifth straight monthly primary fiscal surplus of 2.33 trillion pesos ($2.57 billion) in May, the largest yet under libertarian President Javier Milei who took office in December and ushered in tough austerity.

The result, twinned with a monthly financial fiscal surplus of 1.18 trillion pesos, underscores how Milei's government is doubling down on a pledge to achieve a "zero deficit" this year to right the South American country's embattled economy.

Milei blames years of over-spending and deep fiscal deficits for Argentina's triple digit inflation rate, long-standing capital controls that warp trade, regular debt defaults and poor reputation with global creditors and investors.

"With income that greatly exceeded previous levels, the government's commitment to fiscal balance determined that the level of sustainable spending is maintained in the medium and long term, needed to get in order the national fiscal accounts," the Ministry of Economy said in a statement.

It added that it was the first time the state had registered five straight months of financial fiscal surpluses since 2008.

($1 = 905.5000 Argentine pesos)

(Reporting by Walter Bianchi; Editing by Aida Pelaez-Fernandez)

By Walter Bianchi